Conformationally-controlled biologically active macrocyclic small molecules as motilin antagonists or ghrelin agonists

ABSTRACT

Novel spatially-defined macrocyclic compounds containing specific conformational control elements are disclosed. Libraries of these macrocycles are then used to select one or more macrocycle species that exhibit a specific interaction with a particular biological target. In particular, compounds according to the invention are disclosed as agonists or antagonists of a mammalian motilin receptor and a mammalian ghrelin receptor.

FIELD OF THE INVENTION

This invention relates to spatially-defined macrocyclic compounds with specific conformational control elements. It also relates to the generation of libraries of these macrocycles. These libraries are then used to select one or more macrocycle species that exhibit a specific interaction with a particular biological target.

BACKGROUND OF THE INVENTION

Among the variety of compounds that have consistently been found to possess potent and selective biological activity are natural products and peptides. Indeed, members of these classes have become useful pharmaceutical agents. Unfortunately, each type has limitations that have restricted the wider utility of these structures.

In fact, natural products often have extremely complex structures that are difficult to synthesize, particularly in the combinatorial fashion that would provide access to a greater number of analogues with which to define pharmacophoric elements and best explore modulation of the biological properties of the parent compound. Nevertheless, some efforts have been successful at constructing natural product libraries containing a modest number of analogues.

Peptides, on the other hand, have been at the forefront of the development of combinatorial chemistry due to their ease of synthesis on solid support, the reproducible and high-yielding reactions involved, and the ready availability of starting materials. Peptides being the endogenous ligands for a number of enzymes and receptors, their modification can be performed to develop even more potent agonists or inhibitors of these same receptors and enzymes. In addition, combinatorial peptide libraries have been used to find a number of previously unknown active sequences for a wide array of enzyme and receptor systems.

However, peptidic compounds are plagued by the usual limitations associated with the direct use of peptides as pharmaceuticals, including rapid metabolic degradation by proteases, short pharmacokinetic half-life, difficulty in transport to site of action in tissues and organs, poor oral bioavailability and solubility, potential antigenicity, as well as high manufacturing costs.

Nevertheless, the densely functionalized and structurally diverse nature of peptides is advantageous when seeking new drug molecules. Hence, peptides are primarily used as the starting point or template for the development of new pharmaceutical leads that often results in structures that only partially resemble, if at all, the initial active peptide. In particular, the recognition potential of the amino acid side chains has resulted in attempts to incorporate these side chains into non-peptidic rigid scaffolds that attempt to duplicate the conformational display required for optimal interaction between the molecule and the target, as well as mimic standard protein and peptide secondary structural elements. For example, sugars and aromatic rings have been exploited as rigid scaffolds containing amino acids or analogues as pendant moieties at one or more positions. Compounds and combinatorial libraries utilizing 3- and 4-substituted pyrrolidines as a central template for display of interacting functionality have been disclosed in U.S. Pat. No. 5,646,285 and U.S. Pat. No. 5,891,737.

In another approach, cyclic structures can greatly improve the pharmacological and pharmacokinetic profiles of peptides (Molecular Diversity 2000 (pub. 2002), 5, 289-304). Cyclic peptides analogues offer a number of benefits compared with the corresponding linear analogues, including restricted conformational mobility, defined topology, enhanced stability to proteolytic enzymes and modified polarity. Furthermore, cyclic peptides can enhance potency, selectivity, stability, bioavailability and membrane permeability. The stability to enzymatic degradation of the cyclic structure arises from the difficulty of such molecules to attain the extended conformation required to be recognized as a substrate for peptidases. Very large mixture libraries (10⁸ members or more) of cyclic peptides have been described in WO 98/54577.

However, larger rings are often too flexible and can occupy too many conformations to be useful. Further, their molecular size and resulting physicochemical characteristics do not fit the typical requirements for being “drug-like.” Small cyclic peptides containing the key interacting residues would provide the necessary conformational restriction, but may have other disadvantages, including synthetic difficulty, ease of dimerization, unfavorable ring strain caused by the presence of the preferred trans amide bonds, lack of stability towards metabolism and hydrolysis to release that strain and limited topological diversity.

Most attention in combinatorial chemistry has been devoted to producing diversity in terms of chemical composition. However, essentially no effort has been directed at integrating this with diversity in terms of the crucial three-dimensional structure.

The use of certain tether elements to control conformation was reported in WO 01/25257. However, although those tethers were successful in restricting the conformational display of the molecule, they only were able to duplicate a portion of the spatial region accessible to a linear molecule, which can contain hundreds if not thousands of possible conformations. To better cover the available conformational space, additional tether elements that define new conformations are required. In addition, the tethers in the previous report were generally hydrophobic in nature. This effects key properties of the macrocyclic molecules such as solubility and log P that are known to have an impact on the compound's pharmacological properties, in particular oral bioavailability. Further, variation of these physicochemical properties is often required in order to optimize the desired characteristic of a molecule as a therapeutic agent. As well, the early tethers were rather limited in their chemical functionality. Since this part of the molecule also could have interactions with a biological target in addition to its conformational control function, a greater diversity in the chemical functional groups could prove advantageous. The more chemically diverse tethers of the present invention therefore have been designed to address these limitations of the existing art and provide the following benefits:

-   -   Access to previously inaccessible conformations     -   Modification of physicochemical parameters     -   Improvement of pharmacokinetic profile     -   Additional interacting functionalities for modulation of         biological activity

Growing evidence suggests that molecular rigidity confers favorable pharmacokinetic properties on molecules and leads to improved clinical success (J. Med. Chem. 2003, 46, 1250-1256; J. Med. Chem. 2002, 45, 2615-2623). The tethers of the present invention therefore will be extremely useful in utilizing these macrocyclic molecules in the search for new pharmaceuticals. Examples of the activity that have been exhibited by representative molecules of the invention are provided.

Therefore, there remains a need for specifically designed chemical entities built on a macrocyclic framework, which exploit the three-dimensional conformation changes triggered by peptidic modifications and/or by inserting specific tether-like portions, in their macrocyclic skeleton.

SUMMARY OF THE INVENTION

The present invention is directed towards spatially-defined macrocyclic compounds which incorporate conformational control elements in order to limit their three-dimensional structure to a small number of spatial orientations. These compounds are defined by general formula (1):

wherein

-   -   A₁, A₂, A₃ and A₄ are natural amino acid residues or unnatural         amino acid residues;     -   A₃ and A₄ are optionally present;     -   W is O or —NR₁—, wherein R, is selected from the group         consisting of hydrogen, alkyl, substituted alkyl, acyl and         sulfonyl;     -   T is a bivalent radical chosen from the group consisting of

wherein q₁, q₂, q₃, q₆, q₇, q₈, q₉, q₁₀, q₁₁, q₁₃, q₁₅ and q₁₆ are each independently 1, 2, 3, 4 or 5;

-   -   q₄ and q₁₈ are independently 1 or 2;     -   q₅is 2, 3 or 5;     -   q₁₂ and q₁₄ are each independently 0, 1, 2, 3 or 4;     -   q₁₇ is 0, 1, 2 or 3;     -   P₁, P₂, P₃ P₄ and P₅ are each independently O, S or NH;     -   P₆ is N or CH;     -   P₇ is O or CR₅₂R₅₃;     -   R₃₆ is hydrogen, C₁-C₆ alkyl, benzyl or acyl;     -   R₅₀ and R₅₁ are independently selected from the group consisting         of hydrogen, alkyl, hydroxy, alkoxy, or amino with the proviso         that if one of R₅₀ or R₅₁ is hydroxy, alkoxy or amino, the other         is hydrogen or alkyl;     -   R₅₂ and R₅₃ are independently selected from the group consisting         of hydrogen, alkyl, hydroxy, alkoxy, or amino with the proviso         that if one of R₅₂ or R₅₃ is hydroxyl, alkoxy or amino, the         other is hydrogen or alkyl;     -   R₅₄, R₅₅, R₅₆, R₅₇ and R₅₈ are independently selected from the         group consisting of hydrogen, alkyl, hydroxy, alkoxy, or amino;     -   R_(AA) is a side-chain of a natural amino acid or a side-chain         of an unnatural amino acid;     -   (W) indicates the point of attachment of T to W;     -   and (A₁) indicates the point of attachment of T to A₁.

Libraries of these compounds are then used to select one or more macrocycle species that exhibit a specific interaction with a particular biological target. Such targets include, but are not limited to, enzymes and receptors. More particularly, the macrocyclic libraries of the invention serve as a readily accessible source of diverse macrocyclic compounds for use in identifying new biologically active macrocyclic compounds through pharmaceutical candidate screening assays, for use in studies defining structure/activity relationships, and/or for use in clinical investigation. In particular, compounds of formula (I) are disclosed as agonists or antagonists of a mammalian motilin receptor and a mammalian ghrelin receptor.

While the invention will be described in conjunction with an example embodiment, it will be understood that it is not intended to limit the scope of the invention to such embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. (I) is a general scheme showing one approach to the solid phase synthesis of compounds of the invention.

FIG. (II) is a general scheme showing a second approach to the solid phase synthesis of compounds of the invention.

FIGS. 3-16, 17 a, 17 b, 17 c and 18-19 are synthetic schemes that show routes to specific tethers (T) used for the synthesis of compounds of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The macrocyclic compounds of the present invention incorporate a variety of tethers, thus allowing coverage of a specific section of conformational space. Furthermore, these tethers are selected on the basis of their ability to synthetically produce macrocycles in reasonable yield across a wide range of sequences. Accordingly, the compounds of the invention, which incorporate these tethers, represent a wide variety of different conformations, with some more rigid and others more flexible. In addition, some of the tethers are much more rigid in their conformation, sometimes displaying essentially only one low energy form. In these cases, improved biological results would provide excellent information on the specific, optimum bioactive conformation. Additionally, in contrast to many traditional approaches, the same synthetic routes and methods are employed in this optimization process. The ability to rapidly access such information transforms what is usually an extremely difficult and time intensive task into a much more straight forward undertaking.

As such, this invention permits the simultaneous investigation of chemical and conformational diversity within a single structural framework and therefore possesses great potential for use in increasing the speed and efficiency of research aimed at new pharmaceuticals.

Accordingly, the invention provides macrocyclic compounds of formula (I) wherein A₁, A₂, A₃, A₄, W and T are as defined previously.

In a specific embodiment, there are provided compounds of formula (I), T is chosen from the following bivalent radicals:

wherein Y is selected from hydrogen, alkyl, benzyl or acyl.

The invention also provides compounds of formula 1 wherein at least one of A₁, A₂, A₃ and A₄ can further be a protected natural or unnatural amino acid residue.

The present invention has applicability to a broad range of biological targets that likewise represent diverse therapeutic indications. Active compounds initially generated can be further optimized and refined to eventually provide lead clinical candidates. A further advantage of the invention is that these subsequent steps in the optimization process can be conducted utilizing the same basic chemical synthesis pathway, hence greatly simplifying and speeding up what is typically an extremely time-consuming phase of the overall drug discovery process.

In particular, the invention provides compounds of formula (I)) which are agonists or antagonists of a mammalian motilin receptor and/or a mammalian ghrelin receptor.

Motilin, a linear 22-amino acid peptide, plays a critical regulatory role in the GI physiological system through governing of fasting gastrointestinal motor activity. As such, the peptide is periodically released from the duodenal mucosa during fasting in mammals, including humans. More precisely, motilin exerts a powerful effect on gastric motility through the contraction of gastrointestinal smooth muscle to stimulate gastric emptying, decrease intestinal transit time and initiate phase III of the migrating motor complex in the small bowel. Due to the critical and direct involvement of motilin in control of gastric motility, agents that either diminish (hypomotility) or enhance (hypermotility) the activity at the motilin receptor, are a particularly attractive area for further investigation in the search for new effective pharmaceuticals towards these indications. Macrocyclic antagonists of the motilin receptor are disclosed in U.S. Prov. Pat. Appl. Ser. No. 60/479,223.

Likewise, ghrelin is a key peptide hormone involved in a number of important physiological functions including growth hormone secretion, maintenance of energy balance, appetite and gut motility. As such, antagonists of this receptor have been investigated for treatment of obesity, while ghrelin agonists have interest in treatment of a variety of diseases, including conditions caused by growth hormone deficiency, wasting syndrome, and GI disorders involving dysmotility.

motilin (human, porcine,SEQ ID NO:1) Phe-Val-Pro-Ile-Phe-Thr-Tyr-Gly-Glu-Leu-Gln-Arg- Met-Gln-Glu-Lys-Glu-Arg-Asn-Lys-Gly-Gln ghrelin (human SEQ ID NO:2) Gly-Ser-Ser(Oct)-Phe-Leu-Ser-Pro-Glu-His-Gln-Arg- Val-Gln-Gln-Arg-Lys-Glu-Ser-Lys-Lys-Pro-Pro-Ala- Lys-Leu-Gln-Pro-Arg

EXAMPLES

Synthesis Method

An assortment of synthetic strategies, involving both solution and solid phase techniques, can be used to access the macrocyclic compounds of the invention, several of which have already been disclosed in WO 01/25257.

An outline of a first approach to the solid phase synthesis of the compounds of the invention, using a thioester linker strategy is provided in FIG. (I). A second approach, called ring-closing metathesis (RCM), is also generally outlined in FIG. (II).

In both, the construction involves four phases: first is synthesis of the building blocks, comprising mainly recognition elements for interaction at biological targets, plus the key tether moiety, primarily for control and definition of conformation. These building blocks are assembled together, typically in a sequential fashion, in a second phase employing standard chemical transformations and those described in the Standard Procedures herein. The precursors from the assembly are then cyclized in the third stage, which could involve multiple steps, to provide the macrocyclic structures. Finally, a post-cyclization processing stage involving removal of protecting groups and optional purification then provides the desired final compounds.

General Information

Reagents and solvents were of reagent quality or better and were used as obtained from various commercial suppliers unless otherwise noted. DMF, DCM, DME and THF used are of DriSolv® (EM Science, now EMD Chemicals, Inc., part of Merck KGaA, Darmstadt, Germany) or synthesis grade quality except for (i) deprotection, (ii) resin capping reactions and (iii) washing. NMP used for the amino acid (AA) coupling reactions is of analytical grade. DMF was adequately degassed by placing under vacuum for a minimum of 30 min prior to use. Boc— and Fmoc—protected amino acids and side chain protected derivatives, including those of N-methyl and unnatural amino acids, were obtained from commercial suppliers or synthesized through standard methodologies known to those in the art. Ddz-amino acids were either synthesized by standard methods, or obtained commercially from Orpegen (Heidelberg, Germany) or Advanced ChemTech (Louisville, KY, USA). Bts-amino acids were synthesized by established procedures. Hydroxy acids were obtained from commercial suppliers or synthesized from the corresponding amino acids as described in the literature (Tetrahedron 1989, 45, 1639-1646; Tetrahedron 1990, 46, 6623-6632; J.Org. Chem. 1992, 57, 6239-6256.; J. Am. Chem. Soc. 1999, 121, 6197-6205). Analytical TLC was performed on pre-coated plates of silica gel 60F254 (0.25 mm thickness) containing a fluorescent indicator.

¹H and ¹³C NMR spectra were recorded on a Varian Mercury 300 MHz spectrometer (Varian, Inc., Palo Alto. CA) and are referenced internally with respect to the residual proton signals of the solvent. Information about the conformation of the molecules in solution can be determined utilizing appropriate two-dimensional NMR techniques known to those skilled in the art.

HPLC analyses are performed on a Waters Alliance® system 2695 running at 1 mL/min using an Xterra® MS C18 column (or comparable) 4.6 ×50 mm (3.5 μm). A Waters 996 PDA provided UV data for purity assessment (Waters Corporation, Milford, MA). An LCPackings (Dionex Corporation, Sunnyvale, CA) splitter (50:40:10) allowed the flow to be separated in three parts. The first part (50%) went to a mass spectrometer (Micromass® Platform II MS equipped with an APCI probe) for identity confirmation. The second part (40%) went to an evaporative light scattering detector (ELSD, Polymer Laboratories, now part of Varian, Inc., Palo Alto, CA, PL-ELS-1000™) for purity assessment and the last portion (10%) to a chemiluminescence detector (CLND, Antek® Model 8060, Antek Instruments, Houston, TX, part of Roper Industries, Inc., Duluth, GA) for quantitation and purity assessment. Data was captured and processed utilizing the most recent version of the Waters Millennium® software package (Milford, MA).

Preparative HPLC purifications were performed on final deprotected macrocycles using the Waters FractionLynx® system, on an Xterra® MS C18 column (or comparable) 19 ×100mm (5μm). The injections were done using an At-Column-Dilution configuration with a Waters 2767 injector/collector and a Waters 515 pump running at 2 mL/min. The mass spectrometer, HPLC, and mass-directed fraction collection are controlled via MassLynx® software version 3.5 with FractionLynx®. Fractions (13 ×125 mm tubes) shown by MS analysis to contain the product were evaporated under reduced pressure, most typically on a centrifugal evaporator system (Genevac® HT-4 (Genevac Inc, Valley Cottage, NY), ThermoSavant Discovery®, SpeedVac® or comparable (Thermo Electron Corporation, Waltham, MA) or, alternatively, lyophilized. Compounds were then thoroughly analyzed by LC-MS-UV-ELSD-CLND analysis for identity confirmation, purity and quantity assessment.

Automated medium pressure chromatographic purifications were performed on an Isco CombiFlash® 16× system with disposable silica or Cl8 cartridges that permitted up to sixteen (16) samples to be run simultaneously (Teledyne Isco, Inc., Lincoln, NE). MS spectra were recorded on a Waters Micromass® Platform II or ZQ™ system. HRMS spectra were recorded with a VG Micromass ZAB-ZF spectrometer. Chemical and biological information were stored and analyzed utilizing the ActivityBase® database software (ID Business Solutions Ltd., Guildford, Surrey, UK).

The term “concentrated/evaporated/removed under reduced pressure”. indicates evaporation utilizing a rotary evaporator under either water aspirator pressure or the stronger vacuum provided by a mechanical oil vacuum pump as appropriate for the solvent being removed. “Dry pack” indicates chromatography on silica gel that has not been pre-treated with solvent, generally applied on larger scales for purifications where a large difference in R_(f) exists between the desired product and any impurities. “Flash chromatography” refers to the method described as such in the literature and is applied to chromatography on silica gel (230-400 mesh, EM Science) used to remove impurities some of which may be close in R_(f) to the desired material. Methods specific for solid phase chemistry are detailed separately.

General Methods for Solid Phase Chemistry

These methods can be equally well applied for the synthesis of single compounds or small numbers of compounds, as well as for the synthesis of libraries of compounds of the present invention.

For solid phase chemistry, the solvent choice is important not just to solubilize reactants as in solution chemistry, but also to swell the resin. Certain solvents interact differently with the polymer matrix depending on its nature and can affect this swelling property. As an example, polystyrene (with DVB cross-links) swells best in nonpolar solvents such as DCM and toluene, while shrinking when exposed to polar solvents like alcohols. In contrast, other resins such as PEG-grafted ones like TentaGel®, Rapp Polymere GmbH, Tiibinaen, Germany), maintain their swelling even in polar solvents. For the reactions of the present invention, appropriate choices can be made by one skilled in the art. In general, polystyrene-DVB resins are employed with DMF and DCM common solvents. The volume of the reaction solvent required is generally 1-1.5 mL per 100 mg resin. When the term “appropriate amount of solvent” is used in the synthesis methods, it refers to this quantity. The recommended quantity of solvent roughly amounts to a 0.2 M solution of building blocks (linkers, amino acids, hydroxy acids, and tethers, used at 5 eq relative to the initial loading of the resin). Reaction stoichiometry was determined based upon the “loading” (represents the number of active functional sites, given as mmol / g) of the starting resin.

The reaction can be conducted in any appropriate vessel, for example round bottom flask, solid phase reaction vessel equipped with a fritted filter and stopcock, or Teflon® (DuPont, Wilmington, DE)-capped jar. The vessel size should be such that there is adequate space for the solvent, and that there is sufficient room for the resin to be effectively agitated taking into account that certain resins can swell significantly when treated with organic solvents. The solvent/resin mixture should fill about 60% of the vessel. Take note that all agitations for solid phase chemistry are best conducted with an orbital shaker (for example Forma® Scientific, model 430, 160-180 rpm) (Thermo Electron Corporation, Waltham, MA), except for those where scale makes use of gentle mechanical stirring more suitable, to ensure adequate mixing which is generally accepted to be important for a successful reaction.

The volume of solvent used for the resin wash is a minimum of the same volume as used for the reaction, although more is generally used to ensure complete removal of excess reagents and other soluble residual by-products. Each of the resin washes specified in the Examples should be performed for a duration of at least 5 min with agitation (unless otherwise specified) in the order listed. The number of washings is denoted by “nx” together with the solvent or solution, where n is an integer. In the case of mixed solvent washing systems, both are listed together and denoted solvent 1/solvent 2. The ratio of the solvent mixtures DCM/MeOH and THF/MeOH used in the washing steps is (3:1) in all cases. Other mixed solvents are as listed. After washing, drying in the “standard manner” means that the resin is dried first in air (1 h), and subsequently under vacuum (oil pump usually) until full dryness is attained (minimum 30 min, to O/N).

For representative examples of the new tether moieties disclosed herein, the synthetic routes presented jn FIGS. 3-19 are employed with additional information on selected examples presented further below. Although the routes described represent a specific protection strategy, other suitable protecting groups known in the art can also be employed.

Example T12 Standard Procedure for the Synthesis of Tether T12

For an outline of this route, see FIG. 3. In a 3-L flame-dried three-neck flask, a solution of (aminomethyl)phenylthiobenzyl alcohol (12-0, 96 g, 0.39 mol) in degassed DMF (1 L, 0.4 M) was prepared. To this was added Ddz-N₃ (0.95 eq), followed by 5 TMG (0.39 mol, 49 mL). The reaction was stirred for 10 min, then DIPEA (68 mL, 0.39 mol) added. The mixture was heated at 50° C. under N₂ until TLC indicated no Ddz-N₃ remained (48 h typically). (TLC eluent: EtOAc:Hex 50:50; detection: ninhydrin). Upon completion, to the reaction mixture was added 3 L citrate buffer and the separated aqueous layer extracted with Et₂O (3×1500 mL). The combined organic phase was washed sequentially with citrate buffer (2×200 mL), water (2×200 mL) and brine (2×200 mL). The organic layer was dried over MgSO₄, filtered and the filtrate evaporated under reduced pressure. A dark orange oil was obtained, which was purified by dry-pack. For this procedure, the oil was first dissolved in EtOAc:Hex:DCM:TEA (20:80:1:0.5, v/v/v/v). At this point, a little extra DCM was sometimes required to ensure complete dissolution. The solution was loaded onto the column, then the column eluted with EtOAc:Hex:DCM:Et₃N (20:80:1:0.5) until all the impurities were separated out as indicated by TLC, paying particular attention to that closest to the desired product. The elution was then continued with EtOAc:hexanes:Et₃N 30:70:0.5 (v/v/v) and finally with EtOAc:hexanes:Et₃N (50:50:0.5) to elute the desired product. After removal of the solvent from the fractions containing the product under reduced pressure, the residue was dissolved in the minimum amount of DCM, a three-fold larger volume of hexanes added, then the solvents again evaporated under reduced pressure. This treatment was repeated until an off-white foam was obtained. The latter solidified while drying under vacuum (oil pump). Alternatively, the material yielded a solid after sequential concentration with DCM (1×) and hexanes (2×). Tether T12 was obtained as an off-white solid (85-90% yield).

Example T13 Standard Procedure for the Synthesis of Tether T13

Protected versions of tether T13 are accessed through a route (see FIG. 4) analogous to that described below in more detail for T14, except starting from H-Ser-OEt.HCl, in an overall yield of 14-30% for the 6 step sequence.

¹H NMR (CDCl₃): δ 7.53 (1H, s, RR′C═CH—O), 6.42-6.58 (2H, m, Ph), 6.30-6.38 (1H, m, Ph), 5.40-5.50 (1H, m, NH), 4.57 (2H, s, CH ₂OH), 4.40 (2H, d, CH ₂NHDdz), 3.78 (6H, s, 2X(CH ₃OPh)), 2.23-2.00 (1H, broad, OH), 1.76 (6H, s, RR′C(CH ₃)₂). ¹³C NMR (CDCl₃): δ 162, 161, 155, 149, 141, 136, 103, 99, 82, 57, 56, 39, 29.

Example T14 Standard Procedure for the Synthesis of Tether T14

See FIG. 5 for an outline of the synthetic scheme.

Step T14-1: A solution of 4.4 M sodium methoxide in MeOH (1.0 mL, 4.6 mmol, 0.01 eq) in DCM (300 mL) at 0° C. was diluted with MeOH (35 mL). Dichloroacetonitrile (50 g, 455 mmol, 1.0 eq) was added over 45 min and the resulting mixture stirred at 0° C. for 1 h. L-Cysteine ethyl ester hydrochloride (84.5 g, 455 mmol, 1.0 eq) was added and the reaction stirred O/N at rt. The reaction mixture was diluted with DCM and water. The separated aqueous phase was extracted with DCM (2×). The combined organic phase was dried over MgSO₄, filtered and the filtrate concentrated under reduced pressure. The crude product obtained was acceptable for use in the next step without further purification.

Step T14-2: To a solution of the crude product from step T14-1 (455 mmol based on the theoretical yield) in DCM (500 mL) was added DIPEA (119 mL, 652.5 mmol, 1.5 eq). The resulting mixture was stirred at 50° C. for 5 h, then at rt O/N. The reaction was monitored by TLC (30% EtOAc: 70% Hex; detection: UV and CMA, R_(f)=0.29). Upon completion, the reaction mixture was diluted with DCM and water. The separated aqueous phase was extracted with DCM (2×). The combined organic phase was dried over MgSO₄, filtered and the filtrate concentrated under reduced pressure. ¹H NMR was used to verify the purity and identity of the intermediate compound. The crude product obtained was acceptable for use in the next step without further purification (yield: 100%).

Step T14-3: To a solution of the crude product from step T14-2 (77 g, 375 mmol, 1.0 eq) in DMF (500 mL) was added sodium azide (122 g, 1874 mmol, 5.0 eq). The resulting mixture was mechanically stirred at 65° C. O/N. The reaction was monitored by ¹H NMR because the starting material and product co-eluted on TLC. After completion and cooling to rt, the reaction mixture was diluted with Et₂O and an aqueous solution of saturated NH₄Cl. The separated aqueous phase was extracted with Et₂O (2×). The combined organic phase was washed with brine, dried over MgSO₄, filtered and the filtrate concentrated under reduced pressure. ¹H NMR was used to verify the purity and identity of the intermediate compound. The crude product obtained was acceptable for use in the next step without further purification (yield: 93%).

Step T14-4: To a solution of the crude azide from step T14-3 (73.1 g, 345 mmol, 1.0 eq) in 95% EtOH (700 mL) was added 10% Pd/C (18.3 g, 17.3 mmol, 0.05 eq). Hydrogen gas was bubbled into the suspension for lh, then the resulting mixture stirred O/N with a balloon of hydrogen. The reaction was monitored by TLC (30% EtOAc: 70% Hex; detection: UV and ninhydrin.). The final product remained at the baseline and was positive to ninhydrin. If the reaction was not complete as indicated by TLC, another portion of 10% Pd/C (25% of that originally used) was added, hydrogen bubbled through the solution and the resulting suspension was stirred at rt again O/N. The reaction solution was filtered through a Celite® (World Minerals Inc., Santa Barbara, CA) pad and the pad rinsed thoroughly with EtOAc (until no further product was being recovered as indicated by TLC). ¹H NMR was used to verify the purity and identity of the intermediate compound. The crude product obtained was acceptable for use in the next step without further purification (yield: 93%).

Step T14-5: To a solution of the crude amine from step T14-4 (59.5 g, 320 mmol, 1.0 eq) in degassed (maintained on vacuum pump for 1 h) DMF (200 mL) were sequentially added Ddz-N₃ (93.3 g, 352 mmol, 1.1 eq), TMG (40.1 mL, 320 mmol, 1.0 eq) and DIPEA (55.8 mL, 320 mmol, 1.0 eq). The resulting solution was stirred at rt for 2 d. The reaction was monitored by TLC (100% EtOAc; detection: UV and ninhydrin, R_(f)=0.52). Upon completion, the reaction mixture was diluted with Et₂O and an aqueous solution of citrate buffer (1 M). The separated aqueous phase was extracted with Et₂O (2×). The combined organic phase was washed with citrate buffer (1 M, 2×), water (2×), and brine (2x), then dried over MgSO₄, filtered and the filtrate concentrated under reduced pressure. The crude product was purified by dry-pack (20% EtOAc: 80% Hex to 50% EtOAc: 50% Hex) to give the protected amino ester as a yellow solid. ¹H NMR was used to verify the identity of the intermediate compound (yield: 65%).

Step T14-6: To a solution of the protected amino ester from step T14-5 (10.5 g, 25.7 mmol, 1.0 eq) in THF (150 mL) at 0° C. were added lithium borohydride (1.68 g, 77.1 mmol, 3.0 eq) and MeOH (3.1 mL, 77.1 mmol, 3.0 eq). The resulting mixture was stirred for 1 h, then identical portions of lithium borohydride and MeOH were added. The resulting mixture was stirred at rt for 3 h. The reaction was monitored by TLC (5% MeOH, 95% EtOAc; detection: UV and ninhydrin, R_(f)=0.27. Note that the boronate co-eluted with the starting material, but after quenching, this spot disappeared). The reaction mixture was cooled to 0° C. and water was added very slowly (100-150 mL) to quench the reaction. On larger scales, the salts generated in the reaction were not completely soluble in the aqueous phase at this stage which complicated the extraction and led to lower yields. The resulting mixture was then stirred O/N. The aqueous phase was extracted with EtOAc (4×). The organic phase was dried over MgSO₄, filtered and the filtrate concentrated under reduced pressure. The compound was purified by flash chromatography (3% MeOH, 97% EtOAc) to give tether Ddz-T14 as a pale yellow solid (yield: 67%).

¹H NMR (CDCl₃, ppm): 7.53 (1H, s, RR′C═CH—S), 6.42-6.58 (2H, m, Ph), 6.35 (1H, t, Ph), 5.60-5.50 (1H, m, NH), 4.75 (2H, s, CH ₂OH), 4.60 (2H, d, CH ₂NHDdz), 3.78 (6H, s, 2x(CH ₃OPh)), 2.70-2.50 (1 H, broad, OH), 1.76 (6H, s, RR′C(CH ₃)₂). ¹³C NMR (CDCl₃, ppm): 170, 161, 157,156,149,116, 103, 99, 82, 61, 56, 42, 29.

Example T21 Standard Procedure for the Synthesis of Tether T21

See FIG. 6 for an outline of the synthetic scheme that provides the multi-step protocol for this tether containing methyl ether protection for its secondary hydroxyl groups. Alternative protection that is easier to remove, such as the acetonide, is also possible via this route.

Example T22 Standard Procedure for the Synthesis of Tether T22

An outline of the synthetic scheme that provides efficient routes to the diastereomeric forms of this tether is shown in FIG. 7.

Example T23 Standard Procedure for the Synthesis of Tether T23

The synthetic scheme that provides routes to this tether tether in shown is FIG. 8. Modifications can be used for homologous tethers.

Example T24 Standard Procedure for the Synthesis of Tether T24

The synthetic approach to this tether is shown in FIG. 9.

Example T24 Standard Procedure for the Synthesis of Tether T26

The synthetic scheme that provides this tether is shown in FIG. 10.

MW Calc. for C₁₈H₂₅NO₆, 351.39; MS found (M+H)⁺ 352

Example T27 Standard Procedure for the Synthesis of Tether T27

An outline of the synthetic scheme is shown in FIG. 11.

Step T27-1: Ddz-N-(6-O-TBDPS, 2,3-deoxy-β-D-ribofuranosyl)methylamine (27-1). To a solution of 26-5 (20 g, 0.03mmol) in EtOAc (40 mL) was added 10% rhodium on alumina (200 mg). The mixture was hydrogenated under atmospheric pressure using balloon of H₂ gas. (CAUTION! Hydrogen gas is flammable.) After 12 h, the reaction mixture was filtered through a short pad of Celite® (World Minerals Inc., Santa Barbara, CA) and the filter cake washed with MeOH. The reaction had to be monitored by NMR since the starting material and product had the same R_(f) on TLC. The filtrate and washings were combined and concentrated under reduced pressure. The residue was azeotroped with dry toluene to afford a 98% yield of 27-1, which was used directly in the next step without further purification. MW Calc. for C₃₄H₄₅NO₆Si, 591.8097; MS found (M+H)⁺592.

Step T27-2: Ddz-N-(2,3-deoxy-β-D-ribofuranosyl)methylamine (Ddz-T27). The crude product, 27-1, from the previous step (100 g, 0.17 mol) was dissolved in anhydrous THF (500 mL). To the resulting clear solution was added TBAF (0.25 mol, 250 mL) and the reaction stirred for 2 h at rt. The reaction was monitored by TLC [(EtOAc/hexanes, 1:1,) detection: ninhydrin, R_(f)=0.5]. When the reaction was complete, the solution was poured into ice water and the aqueous solution was extracted with DCM (3×400 mL). The combined organic extract was washed with saturated citrate buffer (1×300 mL), H₂O (200 mL) and brine (200 mL). The washed organic extract was dried over anhydrous Na₂SO₄, filtered and evaporated under reduced pressure to give an oily residue. This residue was purified by flash chromatography (EtOAc/hexanes, 1:1, R_(f)=0.5) to give the protected tether (Ddz-T27) as a syrup (yield 90%). δ

¹H NMR (CDCl₃, 300 MHz): δ 1.61 (m, 1H), 1.74 (s, 6H); 1.80-1.88 (m, 3H); 2.66 (s_(b), 1H); 3.21 (m, 2H); 3.26 (m, 1H), 3.67 (m,1 H); 3.75 (s, 6H); 4.05 (m, 2H);5.25 (m, 1H); 6.32 (m,1H); 6.51 (m, 2H). HPLC (Standard Gradient): Retention time (t_(r)): 6.43 min MW Calc. for C₁₈H₂₇NO₆, 353.4101; MS found (M+H)⁺ 354.

Example T33 Standard Procedure for the Synthesis of Tether T33

An outline of the synthetic scheme towards this chiral tether is shown in FIG. 12. The enantiomers are accessed depending on the configuration of the starting lactic acid derivative with the (R)-isomer coming from (S)-methyl lactate and the (S)-isomer of T33 resulting from (R)-methyl lactate

¹H NMR (CDCl₃): δ 7.18-7.11 (m, 2H), 6.90 (m, 2H), 6.52 (m, 2H), 6.33(m, 1H), 5.09 (bt, 1H), 4.52 (m, 1H), 3.77 (s, 6H), 3.08 (bq, 2H), 2.64 (bt, 2H), 1.75 (m, 8H); 1.27 (bd, 3H) ¹³C NMR (CDCl₃): δ 160.8, 155.5, 149.5, 131.2, 130.6, 127.4, 121.2, 113.3, 103.2, 98,4, 80.7, 74.8, 66.5, 55,4, 40.2, 30.6, 29.3, 29.2, 27.4, 16.1

Example T38 Standard Procedure for the Synthesis of Tether T38

An outline of the synthetic scheme for racemic material is shown in FIG. 13. The enatiomers are accessed through the use of the optically pure propylene oxide enantiomers. Since the center of the epoxide is inverted during the protocol, the (R)-epoxide provides T38(S), while the (S)-epoxide provides T38(R).

¹H NMR (CDCl₃): δ 7.20-7.10, (m, 2H), 6.95-9.80 (m, 2H), 6.55 (bs, 2H), 6.35 (s, 1H), 5.18 (bt, 1H), 4.12 (m, 1H), 3.98 (m, 2H), 3.80 (s, 6H), 3.15 (bq, 2H), 2.65 (t, 2H), 1.98 (bs, 2H), 1.65 (bs, 6H), 1.25 (m, 3H).

Example T39 Standard Procedure for the Synthesis of Tether T39

See FIG. 14 for an outline of the synthetic scheme for racemic product. Enantiomeric versions can be accessed via resolution methodologies or use of an asymmetric Michael addition in the third step.

¹H NMR (CDCl₃): δ 7.11-7.08 (2H, m), 6.86 (1H, t), 6.76 (1H, d), 5.05 (1H, broad), 4.26-3.85 (4H, m), 3.22-3.07 (2H, m), 2.71 (1 H, broad), 1.66-1.60 (2H, m),1.33 (9H, s), 1.17 (3H, d). 13C NMR (CDCl₃): δ 156.1, 135.0, 127.1, 127.0, 121.4, 111.7, 69.9, 61.5, 39.8, 38.4, 28.7, 20.7.

Example T40 Standard Procedure for the Synthesis of Tether T40

An outline of the synthetic scheme for racemic material is shown in FIG. 15, while FIG. 16 outlines the route to both enantiomers involving an enzymatic resolution as the key step.

¹H NMR (CDCl₃): δ 7.11-7.08 (2H, m), 6.86 (1H, t), 6.76 (1H, d), 5.05 (1H, broad), 4.26-3.85 (4H, m), 3.22-3.07 (2H, m), 2.71 (1H, broad), 1.66-1.60 (2H, m), 1.33 (9H, s), 1.17 (3H, d). ¹³C NMR (CDCl₃): δ 156.1, 135.0, 127.1, 127.0, 121.4, 111.7, 69.9, 61.5, 39.8, 38.4, 28.7, 20.7.

Example T41 Standard Procedure for the Synthesis of Tether T41

See FIG. 17( a) for an outline of the synthetic scheme that provides an appropriately protected derivative for use in macrocycle construction via FIG. 1.

¹H NMR (CDCl₃): δ 1.23 (s, 3H), 1.49 (s, 3H), 1.69 (s, 3H), 1.74 (s, 3H), 1.90 (m, 2H), 2.35 (m, 1H), 3.35 (m, 2H), 3.76 (s, 6H), 3.92 (m, 2H), 4.40 (m, 2H), 5.10 (m, 1H), 6.15 (s, 1H), 6.25 (s, 2H). ¹³C NMR (CDCl₃): δ 25.52 (CH₃), 27.53 (CH₃), 28.88 (CH₃), 29.61 (CH₃), 35.92 (CH₂), 42.62 (CH₂), 55.43 (CH₃), 60.60 (CH₂), 82.38 (CH), 83.33 (CH), 83.68 (CH), 84.96 (CH), 98.26 (CH), 103.23 (CH), 118.3 (Cq), 149.50 (Cq), 156.20 (Cq), 160, 02 (Cq) MW Calcd. for C₂₂H₃₃NO₈: 439.50; MS Found: (M+H)⁺ 440

Example T54 Standard Procedure for the Synthesis of Tether T54

See FIG. 17( c) for an outline of the synthetic scheme from a T55 derivative.

¹H NMR (CDCl₃): δ 1.55 (m, 2H), 1.72 (s, 6H), 1.8-2.01 (m, 4H), 2.75 (s_(b), 1H), 3.10 (m, 1H), 3.32 (m, 1H), 3.65 (s, 6H), 3.66 (m, 2H), 3.90-4.01 (m, 2H), 5.30 (m, 1H), 6.30 (s, 1H), 6.50 (s, 2H). ¹³C NMR (CDCl₃): δ 28.04 (CH₂), 29.18 (CH₃), 29.34 (CH₃), 31.69 (CH₂), 38.08 (CH₂), 44.94 (CH₂), 55.41 (CH₃), 61.28 (CH₂), 78.84 (CH), 79.41 (CH), 80.75 (Cq), 98.44 (CH), 103.15 (CH), 149.44 (Cq), 155.64 (Cq), 160.81 (Cq). MW Calcd. for C₁₉H₂₉NO₆: 367.44; MS Found: (M+H)⁺ 368

Example T55 Standard Procedure for the Synthesis of Tether T55

See FIG. 17( b) for an outline of the synthetic scheme.

¹H NMR (CDCl₃): δ 1.66 (s, 3H), 1.71 (s, 3H), 1.82 (m, 1H), 1.89 (m, 1H), 3.26 (m, 2H), 3.77 (s, 6H), 3.80 (m, 2H), 4.84 (m, 1 H), 4.95 (m, 1 H), 5.20 (m, 1 H), 5.70 (m, 1H), 5.85 (m,1H), 6.32 (s, 1H), 6.49 (s, 2H). ¹³C NMR (CDCl₃): δ 29.06 (CH₃), 29.42 (CH₃), 38.73 (CH₂), 44.87 (CH₂), 55.45 (CH₃), 61.01 (CH₂), 80.77 (Cq), 85.84 (CH), 86.25 (CH), 98.28 (CH), 103.28 (CH), 127.84 (CH), 131.95 (CH), 149.42 (Cq), 155.59 (Cq), 160.79 (Cq). MW Calcd. for C₁₉H₂₇NO₆: 365.42; MS Found: (M+H)⁺ 366

Example T56 Standard Procedure for the Synthesis of Precursor (56-1) for Tethers T56 and T57

For some of the tether structures, specifically those arising from the ring-closing metathesis methodology (RCM, FIG. 2), the tether is not added as an already assembled unit, but is constructed during the macrocyclization reaction from appropriate precursor pieces. One such example id shown in FIG. 19 in which 56-1, containing a pendant alkene moiety, will be subjected to RCM whereby the alkene will join with an alkene in another part of the substrate to form the macrocyclic ring and, hence, construct tether T56 (or homologues). Reduction of the double bond in macrocycles containing T56 leads to macrocycles containing T57. Other tethers that were constructed in this manner include T46, T47, T49, and T51.

Table 1 lists the structural features for 60 preferred embodiments of compounds of formula (I).

Table 2 gives the Mass Spectrum analytical data for these compounds.

TABLE 1 Representative Compounds of formula (I) (I)

Cmpd A₁ A₂ A₃ T* 201

T40(S) 202

T40(S) 203

T38(S) 204

T40(R) 205

T40(R) 206

T38(R) 207

T40(S) 208

T38(S) 209

T40 210

T39 211

T40(R) 212

T58 213

T39 214

T40(R) 215

T59(S) 216

T59(R) 217

T38(R) 218

T59(S) 219

T59(R) 220

T33(R) 222

T38 223

T38 224

T41 225

T41 226

T33(S) 227

T33(R) 228

T12 229

T56(Y = H) 230

T57(Y = H) 231

T56(Y = Me) 232

T57(Y = Me) 233

T21(Y = H) 234

T26 235

T12 236

T13 237

T14 238

T12 241

T38 242

T33(R) 243

T33(S) 244

T33(R) 245

T33(S) 246

T39 247

T58 248

T40 249

T21(Y = H) 250

T24 251

T12 252

T27 253

T14 254

T33(R) 255

T33(S) 256

T39 257

T40 258

T58 259

T12 260

T46 261

T47 262

T49 263

T51 264

T51 *Designation in parentheses indicates the absolute configuration (R or S) of the chiral center on the tether. If no configuration is so designated, the center is racemic. Other designations indicate the identity of a variable substituent.

TABLE 2 Mass Spectral Analyses for Representative Compounds of formula I Molecular Monoisotopic MS Found Cmpd Molecular Formula Weight Mass (M + H)⁺ 201 C31H42N7O4F3 633.7 633 634 202 C31H44N5O4F 569.7 569 570 203 C30H42N7O4Cl 600.2 599 600 204 C31H42N7O4F3 633.7 633 634 205 C31H44N5O4F 569.7 569 570 206 C30H42N7O4Cl 600.2 599 600 207 C32H43N4O4Cl 583.2 582 583 208 C32H43N4O4F 566.7 566 567 209 C32H43N4O4Cl 583.2 582 583 210 C31H43N4O4Cl 571.2 570 571 211 C32H43N4O4Cl 583.2 582 583 212 C33H45N4O4Cl 597.2 596 597 213 C31H43N4O4F 554.7 554 555 214 C32H43N4O4F 566.7 566 567 215 C31H41N4O5Cl 585.1 584 585 216 C31H41N4O5Cl 585.1 584 585 217 C32H43N4O4F 566.7 566 567 218 C31H41N4O5F 568.7 568 569 219 C31H41N4O5F 568.7 568 569 220 C32H43N4O4F 566.7 566 567 222 C32H46N4O5 566.7 566 567 223 C32H43N4O4Cl 583.2 582 583 224 C27H39N4O6Cl 551.1 550 551 225 C27H42N4O7 534.6 534 535 226 C31H44N4O5 552.7 552 553 227 C31H44N4O5 552.7 552 553 228 C30H38N6O3S 562.7 562 563 229 C28H41N3O8 547.6 547 548 230 C28H43N3O8 549.7 549 550 231 C30H45N3O8 575.7 575 576 232 C30H47N3O8 577.7 577 578 233 C25H38N4O7 506.6 506 507 234 C25H36N4O5 472.6 472 473 235 C38H42N4O4S 650.8 650 651 236 C24H33N5O5 471.5 471 472 237 C24H33N5O4S 487.6 487 488 238 C33H40N4O4S 588.8 588 589 241 C30H39N4O4F 538.7 538 539 242 C31H44N4O4 536.7 536 537 243 C31H44N4O4 536.7 536 537 244 C30H39N4O4F 538.7 538 539 245 C30H39N4O4F 538.7 538 539 246 C30H39N4O4F 538.7 538 539 247 C31H41N4O4F 552.7 552 553 248 C30H39N4O4F 538.7 538 539 249 C24H33N4O6F 492.5 492 493 250 C26H41N4O3F 476.6 476 477 251 C31H36N4O3S 544.7 544 545 252 C23H34N4O4 430.5 430 431 253 C22H29N5O3S 443.6 443 444 254 C33H45N4O4Cl 597.2 596 597 255 C33H45N4O4Cl 597.2 596 597 256 C33H45N4O4Cl 597.2 596 597 257 C33H45N4O4Cl 597.2 596 597 258 C34H47N4O4Cl 611.2 611 612 259 C35H42N4O3S 598.8 598 599 260 C23H35N4O3F 434.5 434 435 261 C26H39N4O3Cl 491.1 490 491 262 C27H41N4O3Cl 505.1 504 505 263 C28H43N4O3Cl 519.1 518 519 264 C29H45N4O3Cl 533.1 532 533 Notes 1. Molecular formulas and molecular weights (MW) are calculated automatically from the structure via ActivityBase ® software (ID Business Solution, Ltd., Guildford, Surrey, UK) or, for MW only, from the freeware program Molecular Weight Calculator v. 6.32 2. M + H obtained from LC-MS analysis 3. All analyses conducted on material after preparative purification Biological Evaluation for Compounds of the Invention

The compounds of the present invention were evaluated for their ability to interact at the human motilin receptor and the human ghrelin receptor utilizing competitive redioligand binding assays as described in Method B1 and B2, respectively. Further characterization of the interaction can be performed utilizing the functional assays described in Methods B3 and B4 for the motilin and ghrelin receptors, respectively. All of these methods can be conducted, if so desired, in a high throughput manner to permit the simultaneous evaluation of many compounds.

Results for the examination of representative compounds of the present invention using Methods B1 and B2 are presented in Table 3.

Example Method B1 Competitive Radioligand Binding Assay (Motilin Receptor)

Materials:

-   -   Membranes were prepared from CHO cells stably transfected with         the human motilin receptor and utilized at a quantity of 1.5         μg/assay point. [PerkinElmer™ SignalScreen® Product #6110544,         PerkinElmer, Inc. Wellesley, MA]     -   [¹²⁵I]-Motilin (PerkinElmer, #NEX-378); final concentration:         0.04-0.06 nM     -   Motilin (Bachem™, #H-4385, Bachem Bioscience Inc., King of         Prussia, PA.); final concentration: 1 μM     -   Multiscreen® Harvest plates-GF/B (Millipore™, #MAHFB1H60,         Billerica, MA)     -   Deep-well polypropylene titer plate (Beckman Coulter™,#267006,         Fullerton, CA)     -   TopSeal-A™ (PerkinElmer, #6005185, Wellesley, MA)     -   Bottom seal (Millipore, #MATAH0P00)     -   MicroScint-0™(PerkinElmer,#6013611, Wellesley, MA)     -   Binding Buffer: 50 mM Tris-HCl (pH 7.4), 10 mM MgCl₂, 1 mM EDTA,         0.1% BSA         Assay Volumes:     -   150 μL of membranes diluted in binding buffer     -   10 μL of compound diluted in binding buffer     -   10 μL of radioligand ([¹²⁵I]-Motilin) diluted in binding buffer         Final Test Concentrations (N=11) for Compounds:     -   10, 5, 2, 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01, 0.005 μM.         Compound Handling:

Compounds were provided frozen on dry ice at a stock concentration of 10 mM diluted in 100% DMSO and stored at −20° C. until the day of testing. On the test day, compounds were allowed to thaw at room temperature and than diluted in assay buffer according to the desired test concentrations. Under these conditions, the maximum final DMSO concentration in the assay was 0.5%.

Assay Protocol:

In deep-well plates, diluted cell membranes (1.5 μg/mL) are combined with 10 μL of either binding buffer (total binding, N=5), 1 μM motilin (non-specific binding, N=3) or the appropriate concentration of test compound. The reaction is initiated by addition of 10 μl of [¹²⁵I]-motilin (final conc. 0.04-0.06 nM) to each well. Plates are sealed with TopSeal-A™, vortexed gently and incubated at room temperature for 2 hours. The reaction is arrested by filtering samples through pre-soaked (0.3% polyethyleneimine, 2 h) Multiscreen®Harvest plates using a Tomtec® Harvester (Tomtec, Hamden, CT), washed 9 times with 500 μL of cold 50 mM Tris-HCI (pH 7.4), and than plates are air-dried in a fumehood for 30 minutes. A bottom seal is applied to the plates prior to the addition of 25 μL of MicroScint-0 ® to each well. Plates are then sealed with TopSeal-A™ and counted for 30 sec per well on a TopCount® Microplate Scintillation and Luminescence Counter (PerkinElmer, Wellesley, MA) where results are expressed as counts per minute (cpm).

Data are analyzed by GrapbPad™ Prism® (GraphPad Software, San Diego, CA) using a variable slope non-linear regression analysis. K_(i) values were calculated using a K_(d) value of 0.16 nM for [¹²⁵I]-motilin (previously determined during membrane characterization).

$D_{\max} = {1 - {\frac{\begin{matrix} {\text{test~~concentration~~with~~maximal~~displacement} -} \\ \text{non-specific~~binding} \end{matrix}}{\text{total~~binding} - \text{non-specific~~binding}} \times 100}}$ where total and non-specific binding represent the cpm obtained in the absence or presence of 1 μM motilin, respectively.

Example Method B2 Competitive Radioligand Binding Assay (Ghrelin Receptor)

The competitive binding assay at the human growth hormone secretagogue receptor (hGHS-R1a) was carried out analogously to assays described in the literature. (Bednarek M A et al. (2000), Structure-function studies on the new growth hormone-releasing peptide ghrelin: minimal sequence of ghrelin necessary for activation of growth hormone secretagogue receptor 1 a; J Med Chem 43:43704376. Palucki B L et al. (2001), Spiro(indoline-3,4′-piperidine) growth hormone secretagogues as ghrelin mimetics; Bioorg Med Chem Lett 11:1955-1957.)

Materials

-   -   Membranes (GHS-R/HEK 293) were prepared from HEK-293 cells         stably transfected with the human ghrelin receptor (hGHS-Rla).         These membranes were provided by PerkinElmer BioSignal®         (#RBHGHSM, lot#1887, PerkinlElmer, Wellesley, MA) and utilized         at a quantity of 0.71 μg/assay point.     -   [¹²⁵I]-Ghrelin (PerkinElmer, #NEX-388); final concentration:         0.0070-0.0085 nM     -   Ghrelin(Bachem, #H-4864, Bachem Bioscience Inc., King of         Prussia, PA); final concentration: 1 μM     -   Multiscreen® Harvest plates-GF/C (Millipore, #MAHFC1H60,         Billerica, MA)     -   Deep-well polypropylene titer plate (Beckman Coulter, #267006,         Fullerton, CA)     -   TopSeal-A™ (PerkinElmer, #6005185, Wellesley, MA)     -   Bottom seal (Millipore, #MATAH0P00)     -   MicroScint-0™ (PerkinElmer, #6013611, Wellesley, MA)     -   Binding Buffer: 25 mM Hepes (pH 7.4), 1 mM CaCl₂, 5 mM MgCl₂,         2.5 mM EDTA, 0.4% BSA         Assay Volumes

Competition experiments were performed in a 300 μL filtration assay format.

-   -   220 μL of membranes diluted in binding buffer     -   40 μL of compound diluted in binding buffer     -   40 μL of radioligand ([¹²⁵I]-Ghrelin) diluted in binding buffer

Final test concentrations (N=1) for compounds of the present invention:

-   -   10, 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01, 0.005, 0.002, 0.001 μM.         Compound Handling

Compounds were provided frozen on dry ice at a stock concentration of 10 mM diluted in 100% DMSO and stored at −80° C. until the day of testing. On the test day, compounds were allowed to thaw at rt overnight and then diluted in assay buffer according to the desired test concentrations. Under these conditions, the maximal final DMSO concentration in the assay was 0.1%.

Assay Protocol

In deep-well plates, 220 μL of diluted cell membranes (final concentration: 0.71 μg/well) were combined with 40 μL of either binding buffer (total binding, N =5), 1 μM ghrelin (non-specific binding, N =3) or the appropriate concentration of test compound (N =2 for each test concentration). The reaction was initiated by addition of 40 μL of [¹²⁵I]-ghrelin (final conc. 0.0070-0.0085 nM) to each well. Plates were sealed with TopSeal-A™, vortexed gently and incubated at rt for 30 min. The reaction was arrested by filtering samples through Multiscreen® Harvest plates (pre-soaked in 0.5% polyethyleneimine) using a Tomtec®Harvester (Tomtec, Hamden, CT), washed 9 times with 500 μL of cold 50 mM Tris-HCl (pH 7.4, 4° C), and then plates were air-dried in a fumehood for 30 min. A bottom seal was applied to the plates prior to the addition of 25 μL of MicroScint-0™ to each well. Plates were than sealed with TopSeal-A™ and counted for 30 sec per well on a TopCount® Microplate Scintillation and Luminescence Counter (PerkinElmer, Wellesley, MA) using a count delay of 60 sec. Results were expressed as counts per minute (cpm).

Data were analyzed by GraphPad™ Prism® (GraphPad Software, San Diego, CA) using a variable slope non-linear regression analysis. K_(i) values were calculated using a K_(d) value of 0.01 nM for [¹²⁵I]-ghrelin (previously determined during membrane characterization).

D_(max) values were calculated using the following formula:

$D_{\max} = {1 - {\frac{\begin{matrix} {\text{test~~concentration~~with~~maximal~~displacement} -} \\ \text{non-specific~~binding} \end{matrix}}{\text{total~~binding} - \text{non-specific~~binding}} \times 100}}$ where total and non-specific binding represent the cpm obtained in the absence or presence of 1 μM ghrelin, respectively.

Example Method B3 Aequorin Functional Assay (Motilin Receptor)

Materials:

-   -   Membranes were prepared using AequoScreen™ (EUROSCREEN, Belgium)         cell lines expressing the human motilin receptor (cell line         ES-380-A; receptor accession #AF034632). This cell line is         constructed by transfection of the human motilin receptor into         CHO-K1 cells co-expressing G_(α16) and the mitochondrially         targeted Aequorin (Ref #ES-WT-A5).     -   Motilin (Bachem, #H-4385, Bachem Bioscience Inc., King of         Prussia, PA)     -   Assay buffer: DMEM-F12 (Dulbeccoe's Modified Eagles Medium) with         15 mM HEPES and 0.1% BSA (pH 7.0)     -   Coelenterazine (Molecular Probes™, Leiden, The Netherlands)

Final Test Concentrations (N=5) for Compounds:

-   -   10, 3.16,1, 0.316, 0.1 μM.         Compound Handling:

Compounds were provided as dry films at a quantity of approximately 1.2 μmol in pre-formatted 96-well plates. Compounds were dissolved in 100% DMSO at a concentration of 10 mM and stored at −20° C. until further use. Daughter plates were prepared at a concentration of 500 μM in 30% DMSO with 0.1 % BSA and stored at −20° C. until testing. On the test day, compounds were allowed to thaw at room temperature and than diluted in assay buffer according to the desired test concentrations. Under these conditions, the maximum final DMSO concentration in the assay was 0.6%.

Cell Preparation:

Cells are collected from culture plates with Ca²⁺ and Mg²⁺-free phosphate buffered saline (PBS) supplemented with 5 mM EDTA, pelleted for 2 minutes at 1000× g, resuspended in assay buffer (see above) at a density of 5×10⁶ cells/mL and incubated overnight in the presence of 5 μM coelenterazine. After loading, cells were diluted with assay buffer to a concentration of 5×10⁵ cells/mL.

Assay Protocol:

For agonist testing, 50 μl of the cell suspension was mixed with 50 μl of the appropriate concentration of test compound or motilin (reference agonist) in 96-well plates (duplicate samples). The emission of light resulting from receptor activation was recorded using the Functional Drug Screening System 6000 ‘FDSS 6000’ (Hamamatsu Photonics K.K., Japan).

For antagonist testing, an approximate EC80 concentration of motilin (i.e. 0.5 nM; 100 μL) was injected onto the cell suspension containing the test compounds (duplicate samples) 15-30 minutes after the end of agonist testing and the consequent emission of light resulting from receptor activation was measured as described in the paragraph above.

Results are expressed as Relative Light Units (RLU). Concentration response curves were analyzed using GraphPad™Prism® (GraphPad Software, San Diego, CA) by non-linear regression analysis (sigmoidal dose-response) based on the equation E=E_(max) /(1 +EC₅₀/C)n where E is the measured RLU value at a given agonist concentration (C), E_(max) is the maximal response, EC₅₀ is the concentration producing 50% stimulation and n is the slope index. For agonist testing, results for each concentration of test compound were expressed as percent activation relative to the signal induced by motilin at a concentration equal to the EC₈₀ (i.e. 0.5 nM). For antagonist testing, results for each concentration of test compound were expressed as percent inhibition relative to the signal induced by motilin at a concentration equal to the EC₈₀ (i.e. 0.5 nM).

Example Method B4 Aequorin Functional Assay (Ghrelin Receptor)

Materials

-   -   Membranes were prepared using AequoScreen™ (EUROSCREEN, Belgium)         cell lines expressing the human ghrelin receptor (cell line         ES-410-A; receptor accession #60179). This cell line is         constructed by transfection of the human ghrelin receptor into         CHO-KL cells co-expressing G_(□16) and the mitochondrially         targeted Aequorin (Ref #ES-WT-A5).     -   Ghrelin (reference agonist; Bachem, #H-4864,Bachem Bioscience         Inc., King of Prussia,PA)     -   Assay buffer: DMEM (Dulbecco's Modified Eagles Medium)         containing 0.1% BSA (bovine serum albumin; pH 7.0.     -   Coelenterazine (Molecular Probes, Leiden, The Netherlands)

Final test concentrations (N=8) for compounds of the invention:

-   -   10, 1, 0.3, 0.1, 0.03, 0.01, 0.003, 0.001 μM.         Compound Handling

Stock solutions of compounds (10 mM in 100% DMSO) were provided frozen on dry ice and stored at −20° C. prior to use. From the stock solution, mother solutions were made at a concentration of 500 μM by 20-fold dilution in 26% DMSO. Assay plates were then prepared by appropriate dilution in DMEM medium containing 0.1% BSA. Under these conditions, the maximal final DMSO concentration in the assay was <0.6%.

Cell Preparation

AequoScreen™ cells were collected from culture plates with Ca²⁺ and Mg²⁺-free phosphate buffered saline (PBS) supplemented with 5 mM EDTA, pelleted for 2 min at 1000× g, re-suspended in DMEM—Ham's F12 containing 0.1% BSA at a density of 5×10⁶ cells/mL, and incubated overnight at rt in the presence of 5 μM coelenterazine. After loading, cells were diluted with assay buffer to a concentration of 5×10⁵ cells/mL.

Assay Protocol

For agonist testing, 50 μL of the cell suspension was mixed with 50 μL of the appropriate concentration of test compound or ghrelin (reference agonist) in 96-well plates (duplicate samples). Ghrelin (reference agonist) was tested at several concentrations concurrently with the test compounds in order to validate the experiment. The emission of light resulting from receptor activation in response to ghrelin or test compounds was recorded using the Hamamatsu FDSS 6000 reader (Hamamatsu Photonics K.K., Japan).

Analysis and Expression of Results

Results were expressed as Relative Light Units (RLU). Concentration response curves were analyzed using GraphPad Prism (GraphPad Software, San Diego, Calif.) by non-linear regression analysis (sigmoidal dose-response) based on the equation E=E_(max)/(1+EC_(50/)C)n where E was the measured RLU value at a given agonist concentration (C), E_(max) was the maximal response, EC₅₀ was the concentration producing 50% stimulation and n was the slope index. For agonist testing, results for each concentration of test compound are expressed as percent activation relative to the signal induced by ghrelin at a concentration equal to the EC₈₀ (i.e. 3.7 nM). EC₅₀, Hill slope and % E_(max) values are reported.

TABLE 3 Biological Activity of Representative Compounds of formula I Binding Affinity [K_(i) Compound (μM)]¹ Receptor² 201 A motilin (human) 202 A motilin (human) 203 A motilin (human) 204 A motilin (human) 205 B motilin (human) 206 B motilin (human) 207 A motilin (human) 208 A motilin (human) 209 A motilin (human) 210 A motilin (human) 211 A motilin (human) 212 A motilin (human) 213 A motilin (human) 214 A motilin (human) 215 A motilin (human) 216 A motilin (human) 217 B motilin (human) 218 B motilin (human) 219 B motilin (human) 220 B motilin (human) 221 B motilin (human) 222 A motilin (human) 223 A motilin (human) 224 B motilin (human) 226 B motilin (human) 227 B motilin (human) 228 B motilin (human) 235 C motilin (human) 236 B motilin (human) 237 B motilin (human) 241 A ghrelin (human) 242 A ghrelin (human) 243 A ghrelin (human) 244 A ghrelin (human) 245 A ghrelin (human) 246 B ghrelin (human) 247 B ghrelin (human) 248 B ghrelin (human) 251 B ghrelin (human) 254 A ghrelin (human) 255 A ghrelin (human) 256 B ghrelin (human) 257 A ghrelin (human) 258 B ghrelin (human) 259 C ghrelin (human) 260 C ghrelin (human) 261 C ghrelin (human) 262 B ghrelin (human) 263 B ghrelin (human) 264 B ghrelin (human) ¹Activity presented indicated in the following ranges: A = 0.001–0.10 μM, B = 0.1–1.0 μM, C = 1.0–10.0 μM ²Binding conducted using the Standard Methods described in the Examples

Although preferred embodiments of the present invention have been described in detail herein, it is to be understood that the invention is not limited to these precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of the present invention. 

1. A compound having the structure of formula II:

wherein W, A₁, A₂, A₃ and T are defined as below with the NH of A₁ bonded to T, the C═O of A₁ bonded to the NH of A2, the C═O of A2 bonded to the NH of A_(3,) the C═O of A₃ bonded to W, and (W) and (A₁) indicate the site of bonding of T to W and A₁, respectively: W A₁ NH

NH

NH

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W A₂ NH

NH

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W A₃ NH

NH

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W T NH

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2. An antagonist of a mammalian motilin receptor having the following structure:


3. An agonist of a mammalian ghrelin receptor having the following structure:


4. A compound having a structure selected from the following: 